John Gill Commentary Galatians 4:13

"but ye know that because of an infirmity of the flesh I preached the gospel unto you the first time:" — Galatians 4:13 (ASV)

Ye know how, through infirmity of the flesh
Meaning either their infirmity, to which the apostle accommodated himself in preaching the Gospel to them, delivering it in such a manner as suited with their capacities, feeding them with milk, and not with strong meat; or his own infirmity, respecting either some particular bodily infirmity and disorder, as the headache, with which he is said to be greatly troubled; or the weakness of his bodily presence, the mean outward appearance he made, the contemptibleness of his voice, and the great humility with which he behaved; or rather the many reproaches, afflictions, and persecutions which attended him, when, says he,

I preached the Gospel unto you at the first ;
not the law, but the Gospel; and this he did at his first entrance among them, and was the first that preached it to them, and was the means of their conversion; and therefore, being their spiritual Father, they ought to be as he was, and follow him as they had him for an example.